Fire resistant vapor barrier for roof decks and the like



United States Patent Ofi ice 3,141,858 Patented July 21, 1964 3,141,858 FIRE RESISTANT VAPOR BR FOR ROOF DECKS AND THE LIKE George Arthur Fasold, Mount Healthy, and John Glen Blough, Cincinnati, Ohio, assignors to The Philip Carey Manufacturing Company, Cincinnati, Ohio, a corporation of Ohio No Drawing. Filed May 3, 1960, Ser. No. 26,400 6 Claims. (Cl. 260-23) This invention relates to a fire resistant vapor barrier for roof decks and the like and to a plastic sheeting compound from which such a vapor barrier sheet may be produced. This application is a continuation-in-part of copending application Serial No. 652,086, filed April 11, 1957, now abandoned.

The use of a vapor barrier in building construction is well known and well understood. It is necessary to have a film of material which is sufficiently impervious to the transmission of moisture so as to prevent the entrance of such moisture into insulation, either in walls or on the roof. For our purpose we are primarily interested in the use of vapor barriers between roof decks and roof insulation, the purpose of which is to keep moisture from penetrating from the underside into the roof insulation and into the roofing. This condition may occur when the relative humidity within the building and the outside temperatures are right to cause condensation of moisture. A vapor barrier must be placed on the top side of the roof deck before application of insulation and roofing when there is a possibility of these conditions occurring.

It is desirable to have as eflicient a vapor barrier as possible and also highly desirable that such material be extremely fire resistant.

The sheet, according to the present invention, is basically a polyvinyl chloride sheet and the methods of manufacturing such plastic sheets and the apparatus by means of which such sheets are fabricated are both well known and will not be described herein since they are not necessary for an understanding of the present invention. The present invention relates solely to the compound used in preparing the plastic sheet and to a sheet made of the particular compound.

A well known type of polyvinyl chloride plastic sheet currently on the market comprises Parts Percent 20% carbon black In the above compound, the dioctyl phthalate is. the plasticizer and the carbon black is incorporated into the dioctyl phthalate to give the sheet a black color.

A sheet according to the above composition has many desirable qualities and is excellent for many purposes. However, it has only fair resistance to the transmission of moisture vapor and it is not only not fire resistant, but it is flammable so that its use as a vapor barrier in a roof deck, for example, is contradicted.

With the above considerations in mind, it is the principal object of the present invention to provide a compound from which a plastic sheet may be manufactured in a usual manner and to disclose a plastic sheet made from such compound which is highly fire resistant and has improved resistance to moisture vapor transmission to the extent that it is not only acceptable but desirable for its intended use in a roof deck construction.

The objects of the invention are achieved by that combination of ingredients of which we shall now disclose exemplary embodiments.

Briefly, in the practice of our invention, we depart from the above noted composition of matter in two important respects. First, we substitute for the regular plasticizer, that is the dioctyl phthalate, cresyl diphenyl phosphate, and second, we add a substantial percentage of micronized mlca.

Micronized mica is mica which has been finely divided by subjecting it to a high pressure steam jet and is characterized not only by a small particle size of from 5 to 10 microns but by extreme thinness. Mica is ground in three ways. It is ground dry, which produces relatively large particle sizes, or it is ground wet, which produces smaller particle sizes, or it is micronized, which involves grinding with a high pressure steam jet and this permits sliding of the mica crystal plates apart so that the very small particles of mica are in water form in that they are extremely thin, perhaps even of substantially molecular thickness.

Cresyl diphenyl phosphate is the preferred plasticizer because it is fire resistant and compatible with vinyl chloride and because it need not be added in to large quantities in order to achieve its plasticizing function. There are a great many plasticizers listed in a chart 'in Modern Plastics Encyclopedia, 1950, on pages 1066 to 1077. This chart specifically indicates which of the more than 200 commercially known plasticizers listed are compatible with vinyl chloride. From among those which are compatible with vinyl chloride, one skilled in the art can readily pick out those which are fire resistant. A fairly large group of fire resistant plasticizers are the aryl, alkyl, or mixed aryl-alkyl phosphate plasticizers. Furthermore, plasticizers which contain combined chlorine are fire resistant. Examples of these are chlorinated biphenyl and chlorinated paraffin, both of which are compatible with vinyl chloride.

It must be noted that merely the use of a fire resistant plasticizer will not necessarily produce a fire resistant vapor barrier sheet unless micronized mica is used with it. With other mineral fillers there may be some increase in fire resistance of the sheet (but not necessarily so), but the sheet will definitely have inferior resistance to vapor permeance. The requirements for a fire resistant and vapor impermeable sheet according to the present invention are the use of a fire resistant plasticizer compatible with vinyl chloride together with micronized mica.

In order to determine the fire resistance of the sheeting according to our invention, we use a flame test for vinyl plastic films which is a modification of Underwriters Laboratories, Inc. flame tests of flame-resistant fabrics UL-2l4 (First Edition, August 1955). According to the above noted test, the test specimens are approximately 2%" x 10" in size. The specimens are cut from widely separated symmetrically located sections over the entire area of each sample. Half the specimens are cut with the long dimension in the direction with the grain and half the specimens are cut with the long dimension in the direction across the grain. The specimens are conditioned at 70 to F. and 25% to 50% relative humidity for at least 24 hours prior to the test.

The specimens are suspended in clamps which grip the specimens along each edge to expose a strip 2 inches wide by 10 inches long. The specimens are suspended with the long axis vertical with the lower edge one inch above the top of a Bunsen burner of specified dimensions and supplied with gas having specified heating value, and the burner is adjusted to provide luminous flame 3 /2 inches long with the air supply completely shut 0E.

The flame is applied vertically near the middle of the lower end of the specimen for 12 seconds and is then withdrawn. During the flame application and thereafter, the duration of surface flaming is recorded as well as afterburn or afterglow. After the sample has cooled to room temperature and while still supported in the apparatus, the loose ash is poked out of the charred area with a file. The length of char, which is the distance from the bottom of the specimen to the top end of the area which has become brittle enough to be removed by touching it with a wire probe, is also measured.

The commercially available material described above, when tested as just described, burned all the way to the top in five seconds.

When the cresyl diphenyl phosphate was substituted in approximately the same proportion for the dioctyl phthalate, the fire resistance of the sheet improved to the extent that it was possible to leave the flame on for the full 12 seconds of test. There was afterburn for 8 seconds after the flame was removed and the length of char was inches.

When approximately 9% by weight of micronized mica was added, the afterburn was reduced to 7 seconds and the length of char was reduced to 4% inches. When the amount of micronized mica was increased above and the cresyl diphenyl phosphate reduced to about 27%, a great improvement was noted in the fire resistance in that a sample subjected to the above described test exhibited no afterburn and no afterglow and the length of char was only 3% inches. With a further increase in the percentage of micronized mica to almost 30% and a reduction in the cresyl diphenyl phosphate to about 23% the length of char was reduced to 2% inches. The table below illustrates the results obtained.

Polyvinyl Chloride percent 51. 2 43. 7 Cresyl Diphenyl Phosphate do 27. 2 23. 2 Lead Silicate ,do 1. 5 1. 3 Stearic Acid do 0. 4 .3 Micronized Mica .do 16. 6 28. 4 Carbon Black do 3.1 3.1 Afterburn No No Afterglow s No No Length of Char ches" 3% 2% Similarly vapor permeance tests performed at Mellon Institute on the above compositions showed that the resistance to vapor transmission improved as the percentage of mica was increased in the composition. The following table illustrates this. These data were obtained using Procedure C, Desiccant Method 90 F. and Procedure D, Water Method 90 F. from ASTM standard test E96- 53T titled Measuring Water Vapor Transmission of Materials in Sheet Form. The F.I-I.A. requirement for vapor barriers is a maximum vapor permeance of 1 perm when tested by the Desiccant Method. A perm is defined as the number of grains of moisture vapor passing through a square foot of material per hour per inch of mercury vapor pressure differential.

Polyvinyl Chloride "percent" 61. 7 56. 0 51. 2 43. 7 Cresyl Diphenyl Phosphate do 32. 8 29. 8 27.2 23. 2 Lead Silicate do 1. 9 1.7 1. 5 1. 3 Stearic Acid do 0. 5 0. 4 0. 4 0.3 Micronized Mica do 9.1 16.6 28. 4 20% Carbon Black d0 3.1 3.0 3.1 3.1 Vapor Permeance (Perms):

Procedure C, Desiecant Method 1.15 0.78 0. 6O 0. 48

Procedure D, Water Method 2.02 1. 56 1. 42 1. 28

The sheet material is prepared from the above described compound in conventional manner with the use of con-' without departing from the spirit of the invention. We,

therefore, do not intend to limit ourselves except as set forth in the claims which follow.

Having now fully described our invention, what we claim as new and desire to secure by Letters Patent is:

1. A fire resistance sheet material having low vapor permeance, for use as a vapor barrier for roof decks and the like, formed from a compound consisting of from about 40% to about 50% by weight of polyvinyl chloride, from about 20% to about 27% by weight of cresyl diphenyl phosphate, from about 15% to about 30% by weight of micronized mica, and a total of about 5% by weight of lead silicate, stearic acid and a mineral pigment not affected by the other ingredients in the compound.

2. A sheet material according to claim 1, wherein the polyvinyl chloride is present in an amount from about 44% to about 47% by weight, the cresyl diphenyl phosphate is present in an amount from about 23% to about 25% by Weight, and in which the micronized mica is present in an amount between about 23% and 28% by weight.

3. A fire resistant sheet material having a low vapor permeance, for use as a vapor barrier for roof decks and the like, formed of a compound consisting of about 44% by weight of polyvinyl chloride, about 23% by weight of cresyl diphenyl phosphate, about 28% by weight of micronized mica, and a total of about 5% by weight of lead silicate, stearic acid and a mineral pigment not altected by the other ingredients in the compound.

4. A plastic sheeting compound consisting of from about 40% to about 50% by weight of polyvinyl chloride, from about 20% to about 27% by weight of cresyl diphenyl phosphate, from about 15% to about 30% by weight of micronized mica, and a total of about 5% by weight of lead silicate, stearic acid and a mineral pigment not affected by the other ingredients in the compound.

5. A sheeting compound according to claim 4, wherein the polyvinyl chloride is present in an amount between 44% and 47% by weight, the cresyl diphenyl phosphate is present in an amount between 23% and 25% by weight, and the micronized mica is present in an amount between 23% and 28% by Weight.

6. A fire resistant sheeting compound consisting of about 44% by weight of polyvinyl chloride, about 23% by weight of cresyl diphenyl phosphate, about 28% by Weight of micronized mica, and a total of about 5% by weight of lead silicate, stearic acid and a mineral pigment not afiected by the other ingredients in the compound.

References Cited in the file of this patent UNITED STATES PATENTS Simon et al Nov. 20, 1951 OTHER REFERENCES Monsanto Plasticizers, page 21, 1949; Monsanto Chemical Co., St. Louis 4, Mo.

Todd: Some Rheological Aspects of Vinyl Plastisols, Ofiicial Digest, pages 98, 107-116 (February 1952).

Schildknecht: Polymer Processes (article by Todd),

pages 55 863, 567-70, Interscience Pub., New York (May 1956). 

1. A FIRE RESISTANCE SHEET MATERIAL HAVING LOW VAPOR PERMEANCE, FOR USE AS A VAPOR BARRIER FOR ROOF DECKS AND THE LIKE, FORMED FROM A COMPOUND CONSISTING OF FROM ABOUT 40% TO ABOUT 50% BY WEIGHTD OF POLYVINYL CHLORIDE, FROM ABOUT 20% TO ABOUT 27% BY WEIGHT OF CRESY DIPHENYL PHOSPHATE, FROM ABOUT 15% TO ABOUT 30% BY WEIGHT OF MICRONIZED MICA, AND A TOTAL OF ABOUT 5% BY WEIGHT OF LEAD SILICATE, STEARIC ACID AND A MINERAL PIGMENT NOT AFFECTED BY THE OTHER INGREDIENTS IN THE COMPOUND. 